The invention relates to a method of preparing phthalide by the catalytic hydrogenation of phthalides substituted in position 3 with hydroxyl, methoxy or acetoxy groups.
It has already been proposed to transform phthalides substituted with halogen in position 3 to phthalide in the liquid phase at standard pressure or a slight excess pressure, at elevated temperatures and in the presence of a catalyst, such as especially palladium or nickel. For the neutralization of the hydrochloric acid that forms in the reaction, HCl acceptors are added in the reaction (German Patent Application P 26 16 741.9). (corresponding to Ser. No. 783 576).
The hydrochloric acid can also be removed from the reaction mixture with excess hydrogen (German Patent Application P 26 14 294.9). (corresponding to Ser. No. 783 575).